1. Field of the Invention
The present invention relates to touch panels and, particularly, to a carbon nanotube based touch panel and a display device using the same.
2. Discussion of Related Art
Following the advancement in recent years of various electronic apparatuses, such as mobile phones, car navigation systems and the like, toward high performance and diversification, there has been continuous growth in the number of electronic apparatuses equipped with optically transparent touch panels at the front of their respective display devices (e.g., a display such as a liquid crystal panel). A user of any such electronic apparatus operates it by pressing or touching the touch panel with a finger, a pen, a stylus, or a like tool while visually observing the display device through the touch panel. A demand thus exists for touch panels that are superior in visibility and reliable in operation.
Up to the present time, different types of touch panels, including resistance, capacitance, infrared, and surface sound wave types, have been developed. The capacitance-type touch panel has advantages such as high accuracy and excellent transparency, and thus has been widely used.
A conventional capacitance-type touch panel includes a glass substrate, a transparent conductive layer, and four electrodes. The material of the transparent conductive layer is, selected from a group consisting of indium tin oxide (ITO) and antimony tin oxide (ATO). The electrodes are made of metal and separately formed on a surface of the transparent conductive layer. Further, a protective layer is formed on the surface of the transparent conductive layer that faces away from the substrate. The material of the protective layer has insulative and transparent characteristics.
In operation, an upper surface of the touch panel is pressed/touched with a touch tool, such as a user's finger or an electrical pen/stylus. Visual observation of a screen on the liquid crystal display device provided on a backside of the touch panel is provided. In use, due to an electrical field of the user, a coupling capacitance forms between the user and the transparent conductive layer. For high frequency electrical current, the coupled capacitance is a conductor, and thus the touch tool takes away a little current from the touch point. Current flowing through the four electrodes cooperatively replaces the current lost at the touch point. The quantity of current supplied by the four electrodes is directly proportional to the distances from the touch point to the electrodes. A touch panel controller is used to calculate the proportion of the four supplied currents, thereby detecting coordinates of the touch point on the touch panel.
The optically transparent conductive layer (e.g., ITO layer) is generally formed by means of ion-beam sputtering, and this method is relatively complicated. Furthermore, the ITO layer has generally poor mechanical durability, low chemical endurance, and uneven resistance over an entire area of the touch panel. Additionally, the ITO layer has relatively low transparency. All the above-mentioned problems of the ITO layer tend to yield a touch panel with somewhat low sensitivity, accuracy, and brightness.
What is needed, therefore, is to provide a durable touch panel with high sensitivity, accuracy, and brightness, and a display device using the same.